Direct positive silver halide emulsions containing a 5 nitro -2- arylindole nucleus

ABSTRACT

CYANINE DYES WHICH FEATURE A 5-NITRO-2-ARYLINDOLE NUCLEUS, AND PHOTOGRAPHIC SILVER HALIDE EMULSIONS CONTAINING THEM, ARE PROVIDED. THE DYES ARE PREPARED FROM THE NOVEL INTERMEDIATES 5-NITRO-3-ARYLINDOLE OR 3-FORMYL-5-NITROARYLINDOLE. A NITRO GROUP CAN BE SUBSTITUTED ON A 2-ARYLINDOLE BY REACTING IT WITH SODIUM NITRATE IN SULFURIC ACID. A 3-FORMUL-5-NITRO-2-ARYLINDOLE CAN BE PREPARED BY REACTING DIMETHYLFORMAMIDE AND PHOSPHORYL CHLORIDE WITH A 5NITRO-2-ARYLINDOLE, FOLLOWED BY HYDROLYSIS.

United States Patent 01 Ffice 3,582,343 Patented June 1., 1971 3,582,343 DIRECT POSITIVE SILVER HALIDE EMULSIONS CONTAINING A NITRO 2 ARYLINDOLE NUCLEUS John D. Mee, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y. No Drawing. Continuation-impart of applications Ser. No. 677,043, Oct. 23, 1967, and Ser. No. 746,261, July 22, 1968. This application Aug. 23, 1968, Ser. No. 754,965

Int. Cl. G03c 1/10, U28, U40 US. Cl. 96-106 24 Claims ABSTRACT OF THE DISCLOSURE Cyanine dyes which feature a 5-nitro-2-arylindole nucleus, and photographic silver halide emulsions containing them, are provided. The dyes are prepared from the novel intermediates 5-nitro-2-arylindole or 3-formyl-5-nitroarylindole. A nitro group can be substituted on a 2-arylindole by reacting it with sodium nitrate in sulfuric acid. A 3-formyl-5-nitro-2-arylindole can be prepared by reacting dimethylformamide and phosphoryl chloride with a 5- nitro-2-arylindole, followed by hydrolysis.

This application is a continuation-in-part of my US. patent application Ser. No. 746,261, filed July 22, 1968, now abandoned and my US. patent application Ser. No. 677,043, filed Oct. 23, 1967, now abandoned, both entitled Novel Dyes, Dye Intermediates, and Photographic Emulsions.

This invention relates to novel photographic materials, and more particularly to a new class of cyanine dyes, and to new and improved direct positive photographic silver halide emulsions containing one or more of these new dyes.

Direct positive images have been prepared with certain types of photographic silver halide emulsions: For example, photographic emulsions have been proposed for this purpose comprisng an electron acceptor and silver halide gains that have been fogged with a combination of a reducing agent and a compound of a metal more electropositive than silver. One of the advantages of such direct positive emulsions is that the high-light areas of the images obtained with these materials are substantially free from fog. However, known materials of this type have not exhibited the high speed required for many applications of photography. Also, such known materials have not shown the desired selective sensitivity, especially to radiation in the green to red region of the spectrum. Furthermore, in some instances as with known indole cyanine dyes, the inclusion of color-forming couplers or colored couplers in such emulsions has tended to reduce the sensitivity thereof in proportion to the length of the holding time, i.e., the time period from actual making the coating and curing the emulsion. This is a decided disadvantage since such emulsions cannot be held for any substantial period of time but must be coated immediately as formulated. It is apparent, therefore, that there is need in the art for improved direct positive photographic emulsions having not only good speed and selective sensitivity, but having, in addition, desirable holding or keeping stability.

It is, accordingly, an object of this invention to provide a new class of cyanine dyes which overcome the shortcomings of the above mentioned prior art dyes. Another object is to provide novel direct positive photographic silver halide emulsions, and more particularly fogged direct positive emulsions, containing one or more of the new cyanine dyes of this invention. Another object of this invention is to provde novel emulsions as above containing, in addition, a color former, Another object of this invention is to provide photographic elements comprising a support having thereon at least one layer containing a novel direct positive emulsion of this invention. Another object of this invention is to provide methods for preparing such novel dyes and photographic materials of this invention. Other objects of this invention will be apparent from this disclosure and the appended claims.

I have now found that cyanine dyes derived from nitro substituted 2-arylindoles are outstanding electron acceptors and spectral sensitizers for direct positive type photographic silver halide emulsions. They provide superior reversal systems, especially with fogged silver halide emul sions, that are characterized by both good speed and desired sensitivity to radiation in the green to red region of the spectrum with maximum sensitivity occurring in most cases in the region of about 540-640 mm. I have found further that the inclusion of color-forming couplers in these novel direct positive emulsions results in unexpectedly desirable holding or keeping stability of the emulsion melts. In other words, there is obtained a great reduction in unsensitizing on holding the incorporated coupler emulsion melt during the coating operation, as compared with similar emulsions made with related indole dyes. The images produced with these novel direct positive emulsions of the invention are clear and sharp, and of excellent contrast.

The new class of cyanine dyes of the invention includes those comprising first and second 5- to 6-membered nitrogen containing heterocyclic nuclei joined by a methine I NO:

wherein n represents a positive integer of from 1 to 2; R represents a hydrogen atom, an alkyl group (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, cyclohexyl, decyl, etc., in aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, etc., a heterocyclic group such as a thienyl group, and the like, at least one R representing hydrogen; R and R each represents an alkyl group, including substituted alkyl, (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups, (preferably a substituted lower alkyl containing from 1 to 4 carbon atoms), such as a hydroxyalkyl group, e.g., p-hydroxyethyl, w-hydroxybutyl, etc., an

alkoxyalkyl group, e.g., fi-methoxyethyl, w-butoxybutyl, etc., a carboxyalkyl group e.g., fl-carboxyethyl, w-carboxy butyl, etc., a sulfoalkyl group, e.g., fi-sulfoethyl, w-sulfO- butyl, etc., a sulfatoalkyl group, e.g., fl-sulfatoethyl, wsulfatobutyl, etc., an acyloxyalkyl group, e.g., B-acetoxyethyl, 'y-acetoxypropyl, w-butyryloxybutyl, etc., an alkoxycar-bonylalkyl group, e.g., [i-methoxycarbonylethyl, wethoxycarbonylbutyl, etc., or an aralkyl group, e.g., benzyl, phenethyl, etc., and the like; R represents an alkyl group (e.g., any of those referred to above) or an alkenyl group, e.g., allyl, l-propenyl, 2-butenyl, etc., or an aryl group e.g., phenyl, tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc.; R represents an aryl group, e.g., phenyl, tolyl, naphthyl, chlorophenyl, etc.; R represents a hydrogen atom, an alkyl group (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, decyl, etc., an alkoxy group (preferably containing from 1 to 4 carbon atoms) e.g., methoxy, butoxy, etc., an aryloxy group, e.g., phenoxy, tolyloxy, etc., a halogen atom, e.g., chlorine or bromine, a nitro group, etc.; X represents an acid anion, e.g., chloride, bromide, iodide, sulfamate, perchlorate, ptoluenesulfonate, methyl sulfate, etc.; and Z represents the non-metallic atoms necessary to complete a desensitizing heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring selected from the group including 3. nitrobenzothiazole nucleus, e.g., S-nitrobenzothiazole, 6-nitrobenzothiazole, 5-chloro-6-nitrobenzothiazole, etc.; a nitrobenzoxazole nucleus, e.g., S-nitrobenzoxazole, 6-nitrobenzoxazole, S-chloro-6-nitrobenzoxazole, etc.; a nitrobenzoselenazole nucleus, e.g., S-nitrobenzoselenazole, 6- nitrobenzoselenazole, 5 chloro 6-nitrobenzoselenazole, etc.; an imidazo[4,5-b1quinoxaline nucleus, etc., imidazo- [4,5 -b] quinoxaline, 1, 3-dialkylimidazo [4,5 -b] quinoxaline such as 1,3-diethylimidazo[4,5-b1quinoxaline, 6-chloro- 1,3-diethylimidazo[4,5-b]quinoxaline, etc., 1,3-dialkenylimidazo[4,5-b]quinoxaline such as 1,3-diallylimidazo- [4,5-b1quinoxaline, 6,7 dichloro 1,3 diallylimidazo [4,5-b]quinoxaline, etc., 1-3-diarylimidazo[4,5-b]quinoxaline such as 1,3-diphenylimidazo[4,5-b]quinoxaline, 6- chloro-1,3-diphenylimidazo[4,5-b]quinoxaline, etc.; a 3,3- dialkyl 3H pyrrolo[2,3-b]pyridine nucleus, e.g., 3,3-dimemethyl 3H pyrrolo[2,3-b] pyridine, 3,3 diethyl-3H- pyrrolo[2,3-b]pyridine, etc.; a 3,3 dialkyl-3H-nitroindole, e.g., 3,3-dimethyl-5-nitro-3H-indole, 3,3-diethyl-5- -nitro-3H-indole, 3,3-dimethyl-6-nitro-3H-indole, etc.; a thiazolo[4,5-b]quinoline nucleus; or a nitroquinoline nulceus, e.g., S-nitroquinoline, fi-nitroquinoline, etc.; and the like. Other desensitizing nuclei defined by Z in above Formula II that are useful include nitrothiazole, nitronaphthothiazole, nitrooxazole, nitronaphthoxazole, nitroselenazole, nitronaphthoselenazole, and nitropyridine nuclei. Dyes of Formula II wherein Z represents the atoms required to complete an imidazo[4,5-b]quinoxaline nucleus are especially useful and are the preferred dye species of the invention.

Typical representive dye salts of this invention include:

1,1-dimethyl-5,5'-dinitro-2,2-diphenyl-3,3-indolocarbocyanine salt 1,1'-dibutyl-5,5'-dinitro-2,2'-diphenyl-3,3-indolocarbocyanine salt 5-cl1loro-8-ethyl- 1, l'-dimethyl-5-nitro-2,2'-diphenyl-3 ,3

indolcarbocyanine salt 1,1'-dimethyl-S-nitro-S'-phen0Xy-2,2',8-tripl1enyl-3,3

indolocarbocyanine salt 8-cyclohexyl-5-methoxy-1, 1-dimethyl-5 -nitro-2,2'-di' phenyl-3,3-indolocarbocyanine salt 5-etl1yl-1,1-dimethyl-5'-nitro-2,2'-diphenyl-3 ,3 '-indolcarbocyanine salt 1,1'-dimethyl-5-nitro-2,2-diphenyl-3,3-indolocarbocyanine salt 3'-ethyl-1-methyl-5,6-dinitro-Z-phenyl-3-indolothiacarbocyanine salt 3-ethyl-1-methy1-5,6'-dinitro-2-phenyl-3-indoloselenacarbocyanine salt 3'-ethy1-1-methyl-5,6-dinitro-2-phenyl-3-indolooxacarbocyanine salt 1, 3-diethyl- 1 '-methyl-5 '-nitro-2-phenylimidazo [4,5 -b] quinoxalino-3'-indolocarbocyanine salt 1 '-methyl-5 '-nitro- 1 ,2,3-triphenylimidazo [4,5 -b] quinoxalin0-3-indolocarbocyanine salt 1,1,3 ,3 -tetramethyl-S-nitro-2-phenyl-3 -indolopyrrolo- [2,3-b1pyridocarbocyanine sale 1, 1 '-dimethyl-5 -nitro-2-phenyl-3 -indolothiazolo [4,5 -b] quinolinocarbocyanine salt The cyanine dyes of the invention defined above are powerful electron acceptors for direct positive photographic silver halide emulsions. In addition, they are also useful desensitizers in emulsion used in the process described in Stewart and Reeves, U.S. Pat. No. 3,250,618, issued May 10, 1966.

As used herein and in the appended claims, desensitizing nucleus refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to gelatin silver chlorobromide emulsion containing 40 mole percent chloride and 60 mole percent bromide, at a concentration of from 0.01 to 0.2 gram dye per mole of silver, cause by electron trapping at least about an percent loss in the blue speed of the emulsion when sensitometrically exposed and developed three minutes in Kodak developer D-19 at room temperature. Advantageously, the densensitizing nuclei are those which, when converted to a symmetrical carbocyanine dye and tested as just described essentially completely densenitize the test emulsion to blue radiation (i.e., cause more than about to loss of speed to blue radiation).

The symmetrical cyanine dyes defined by Formula I above wherein R is a S-nitro group are conveniently prepared by reacting a mixture comprising (1) an indole of the formula:

III. H

wherein R and R are as previously defined, with (2) a compound such as 1,3,3-trimethoxypropene, in the presence of (3) a strong acid HX such as a mineral acid or an organic sulfonic acid, e.g., hydrobromic, perchloric, p-toluenesulfonic, etc. acids, in an inert solvent medium such as hot glacial acetic acid, in the proportions of about 2 moles of (1) and at least 1 mole of each of (2) and (3). The crude dyes obtained are purified by one or more recrystallizations from appropriate solvent such as methanol.

The unsymmetrical cyanine dyes defined by Formula I above wherein R is a substituent other than a 5-nitro group are prepared by reacting an indole of the formula:

wherein R, R, R and R are as previously defined, except that R, in this case does not include the S-nitro group, with an indole of Formula V in the presence of a strong acid and in the absence of trimethoxypropene. In a variation, 21 similar procedure can be used to prepare related chain-substituted dyes by reacting a compound similar to Formula V, but which is not nitro substituted,

wherein R and R are as previously defined, with (2) a heterocyclic compound of the formula:

wherein 11, R X and Z are previously defined, in approximately equimolar proportions of (1) and (2), in an inert solvent medium such as hot acetic anhydride. The crude dye obtained is purified by one or more recrystallizations from appropriate solvents such as methanol.

The intermediates defined by Formula III above are readily prepared from an indole of the formula:

VII.

C-Ra

wherein R and R are as previously defined, by reaction with sodium nitrate, in approximately equimolar proportions, in a concentrated sulfuric acid medium, at temperatures not exceeding acid, the solution is chilled, and the sodium nitrate dissolved in sulfuric acid added dropwise with stirring, and ice-bath cooling. The nitrated indole obtained is purified by one or more recrystallizations from an appropriate solvent such as dimethylformamide.

The formyl intermediates defined by Formula V above are prepared from those of Formula III by the use of the Vilsmeier reagent (HCON(CH /POCl in approximately equimolar proportions of (1) the starting indole and (2) phosphoryl chloride. Preferably, the phosphoryl chloride is added to the dimethylformamide, this solution is cooled, and the indole compound is then added, and the mixture is stirred at 40 C. for 30 minutes or more. The reaction mixture is then poured into ice water and neutralized with an aqueous solution of an alkali metal hydroxide such as sodium hydroxide, followed by heating the mixture, cooling, collecting the solid and washing with water.

In accordance with the invention, novel and improved direct positive photographic silver halide emulsions are prepared by incorporating one or more of the cyanine dyes of the invention into a suitable fogged silver halide emulsion. The emulsion can be fogged in any suitable manner, such as by light or with chemical fogging agents, e.g., stannous chloride, formaldehyde, thiourea dioxide,

6 and the like. The emulsion may be fogged by the addition thereto of a reducing agent, such as thiourea dioxide, and a compound of a metal more electropositive than silver, such as a gold salt, for example, potassium chloroaurate, as described in British Pat. 723,019 (1955).

Typical reducing agents that are useful in providing such emulsions include stannous salts, e.g., stannous chloride, hydrazine, sulfur compounds such as thiourea dioxide, phosphonium salts such as tetra(hydroxymethyl) phosphonium chloride, and the like. Typical useful metal compounds that are more electropositive than silver include gold, rhodium, platinum, palladium, iridium, etc., preferably in the form of soluble salts thereof, e.g., potassium chloroaurate, auric chloride, (NH PdCl and the like.

Useful concentrations of reducing agent and metal compound (e.g., metal salt) can be varied over a considerable range. As a general guideline, good results are obtained using about .05 to 40 mg. reducing agent per mole of silver halide and 0.5 to 15.0 mg. metal compound per mole of silver halide. Best results are obtained at lower concentration levels of both reducing agent and metal compound.

The concentration of added dye can vary widely, e.g., from about 50 to 2000 mg. and preferably from about 400 to 800 mg. per mole of silver halide in the direct positive emulsions.

As used herein, and in the appended claims, fogged refers to emulsions containing silver halide grains which produce a density of a least 0.5 when developed, without exposure, for 5 minutes at 68 F. in developer Kodak DK-SO having the composition set forth below, when the emulsion is coated at a silver coverage of 50 mg. to 500 mg. per square foot.

DEVELOPER G. N-methyl-p-aminophenol sulfate 2.5 Sodium sulfite (anhydrous) 30.0 Hydroquinone 2.5 Sodium metaborate 10.0 Potassium bromide 0.5

Water to make 1.0 l.

The dyes of this invention are also advantageously incorporated in direct positive emulsions of the type in which a silver halide grain has a water-insoluble silver salt center and an outer shell composed of a fogged waterinsoluble silver salt that develops to silver without exposure. The dyes of the invention are incorporated, preferably, in the outer shell of such emulsions. These emulsions can be prepared in various ways, such as those described in Berriman U.S. Pat. 3,367,778, issued Feb. 6, 1968. For example, the shell of the grains in such emulsions may be prepared by precipitating over the core grains a lightsensitive water-insoluble silver salt that can be fogged and which fog is removable by bleaching. The shell is of sufficient thickness to prevent access of the developer used in processing the emulsions of the invention to the core. The silver salt shell is surface fogged to make it developable to metallic silver with conventional surface image developing compositions. The silver salt of the shell is sufliciently fogged to produce a density of at least about 0.5 when developed for 6 minutes at 68 F. in Developer A below when the emulsion is coated at a silver coverage of mg. per square foot. Such fogging can be effected by chemically sensitizing to fog with the sensitizing agents described for chemically sensitizing the core emulsion, high intensity light and the like fogging means well known to those skilled in the art. While the core need not be sensitized to fog, the shell is fogged. Fogging by means of a reduction sensitizer, a noble metal salt such as gold salt plus a reduction sensitizer, a sulfur sensitizer, high pH and low pAg silver halide precipitating conditions, and the like can be suitably utilized. The shell portion of the subject grains can also be coated prior to fogging.

7 DEVELOPER A G. N-methyl-p-aminophenol sulfate 2.5 Ascorbic acid 10.0 Potassium metaborate 35.0 Potassium bromide 1.0

Water to 1 liter. pH of 9.6.

Before the shell of water-insoluble silver salt is added to the silver salt core, the core emulsion is first chemically or physically treated by methods previously described in the prior art to produce centers which promote the deposition of photolytic silver, i.e., latent image nucleating centers. Such centers can be obtained by various techniques as described herein. Chemical sensitization techniques of the type described by Antoine Hautot and Henri Sauvenier in Science et Industries Photographiques, vol. XXVIII, January 1957, pages 1 to 23 and January 1957, pages 57 to 65 are particularly useful. Such chemical sensitization includes three major classes, namely, gold or noble metal sensitization, sulfur sensitization, such as by a labile sulfur compound, and reduction sensitization, e.g., treatment of the silver halide with a strong reducing agent which introduces small specks of metallic silver into the silver salt crystal or grain.

The dyes of this invention are highly useful electron acceptors in high speed direct positive emulsions comprising fogged silver halide grains and a compound which accepts electrons, as described and claimed in Illingsworth U.S. patent application Ser. No. 619,936, filed Mar. 2, 1967, and titled Photographic Reversal Materials Case C. The fogged silver halide grains of such emulsions are such that a test portion thereof, when coated as a photo graphic silver halide emulsions on a suport to give a maximum density if at least about one upon processing for six minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for six minutes at about 68 F. in Kodak DK-SO developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide50 mg. Acetic acid (glacial)3.47 cc. Sodium acetate1l.49 mg. Potassium bromidel 19 mg. Water to1 liter.

The grains of such emulsions will lose at least about 25% and generally at least about 40% of their fog when bleached for ten minutes at 68 F. in a potassium cyanide bleach composition as described herein. This fog loss can be illustrated by coating the silver halide grains as a photographic silver halide emulsion on a support to give a maximum density of at least 1.0 upon processing for six minutes at about 68 F. in Kodak DK-50 developer and comparing the density of such a coating with an identical coating which is processed for six minutes at 68 F. in Kodak DK-SO developer after being bleached for about 10 minutes at 68 F. in the potassium cyanide bleach composition. As already indicated, the maximum density of the unbleached coating will be at least 30% greater, generally at least 60% greater, than the maximum density of the bleached coating.

The silver halides employed in the preparation of the photographic emulsions useful herein include any of the photographic silver halides as exemplified by silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide, silver chlorobromide, and the like. Silver halide grains having an average grain size less than about one micron, preferably less than about 0.5 micron, give particularly good results. The silver halide grains can be regular and can be any suitable shape such as cubic or octahedral, as described and claimed in Illingsworth U.S. patent application Ser. No. 619,009, filed Mar. 2, 1967, and titled Direct Positive Photographic Emulsions Case A, now U.S. Pat. No. 3,501,306. Such grains advantageously have a rather uniform diameter frequency distribution, as described and claimed in Illingsworth U.S. patent aplication Ser. No. 619,948, filed Mar. 2, 1967, and titled Photographic Reversal Emulsions Case B, now U.S. Pat. No. 3,501,305. For example, at least by weight, of the photographic silver halide grains can have a diameter which is Within about 40%, preferably within about 30% of the mean grain diameter. Mean grain diameter, i.e., average grain size, can be determined using conventional methods, e.g., as shown in an article by Trivelli and Smith entitled Empirical Relations Between Sensitometric and Size-Frequency Characteristics in Photographic Emulsion Series in The Photographic Journal, vol. LXXIX, 1949, pages 330-338. The fogged silver halide grains in these direct-positive photographic emulsions of this invention produce a density of at least 0.5 when de veloped Without exposure for five minutes at 68 F. in Kodak DK-SO developer when such an emulsion is coated at a coverage of 50 to about 500 mg. of silver per square foot of support. The preferred photographic silver halide emulsions comprise at least 50 mole percent bromide, the most preferred emulsions being silver bromoiodide emulsions, particularly those containing less than about ten mole percent iodide. The photographic silver halides can be coated at silver coverages in the range of about 50 to about 500 milligrams of silver per square foot of support.

In the preparation of the above photographic emulsions, the dyes of the invention are advantageously incorporated in the washed, finished silver halide emulsion and should, of course, be uniformly distributed throughout the emulsion. The methods of incorporating dyes and other addenda in emulsions are relatively simple and well kIlOIWH to those skilled in the art of emulsion making. For example, it is convenient to add them from solutions in appropriate solvents, in which case the solvent selected should be completely free from any deleterious effect on the ultimate light-sensitive materials. Methanol, isopropanol, pyridine, water, etc., alone or in admixtures, have proven satisfactory as solvents for this purpose. The type of silver halide emulsions that can be sensitized with the new dyes include any of those prepared with hydrophilic colloids that are known to be satisfactory for dispersing silver halides, for example, emulsions comprising natural materials such as gelatin, albumin, agar-agar, gum arabic, alginic acid, etc. and hydrophilic synthetic resins such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose ethers, partially hydrolyzed cellulose acetate, and the like.

The binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds. Such compounds are disclosed, for example, in U.S. Pats. 3,142,568; 3,193,386; 3,062,674 and 3,220,844 and include the water insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

The dyes, reducing agents and metal compounds of the invention can be used with emulsions prepared, as indicated above, with any of the light-sensitive silver halide salts including silver chloride, silver bromide, silver chlorobromide, silver bromoiodide, silver chlorobromoiodide, etc. Particularly useful are direct positive fogged emulsions in which the silve salt is a silver bromohalide comprising more than 50 mole percent bromide. Certain dyes of this invention are also useful in emulsions which contain color formers.

The novel emulsions of this invention may be coated on any suitable photgoraphic support, such as glass, film base such as cellulose acetate, cellulose acetate butyrate, polyesters such as poly(ethylene terephthalate), paper baryta coated paper, polyolefin coated paper, e.g., polyethylene or polypropylene coated paper, which may be electron bombarded to promote emulsion adhesion, to produce the novel photographic elements of the invention.

The invention is further illustrated by the following examples.

EXAMPLE 1 1-methyl-5-nitro-2-phenylindole (1.26 g., 2 mols.) and p-toluenesulfonic acid monohydrate, (1 mol. +10%) are dissolved in boiling acetic acid (10 ml.) 1,3,3-trimethoxypropene (1.00 g., 1 mol. +200%) is added, with stirring. The mixture is allowed to stand at room temperature for several hours, then the solid is collected and washed with ether. After one recrystallization from methanol, the yield of purified dye is 0.42 g. (24% M.P. 205-6 C., dec.

The above prepared dye containing two desensitizing 1-methyl-5-nitro-2-phenylindole nuclei is photographically tested for its usefulness as an electron acceptor and spectral sensitizer for fogged direct positive photographic silver halide emulsions by the following procedure.

A gelatin silver bromoiodide emulsion (2.5 mole percent of the halide being iodide) and having an average grain size of about 0.2 micron is prepared by adding an aqueous solution of potassium bromide and potassium iodide, and an aqueous solution of silver nitrate, simultaneously to a rapidly agitated aqueous gelatin solution at a temperature of 70 C., over a period of about minutes. The emulsion is chill-set, shredded and washed by leaching with cold water in the conventional manner. The emulsion is reduction-gold fogged by first adding 0.2 mg. of thiourea dioxide per mole of silver and heating for minutes at C. and then adding 4.0 mg. of potassium chloroaurate per mole of silver and heating for 60 minutes at 65 C. The above prepared dye, 1,1-dimethyl-5,5'- dinitro-2,2'-diphenyl-3,3'-indolocarbocyanine p toluenesulfonate is then added to the above fogged emulsion in amount sufficient to give a concentration as indicated in Table I hereinafter, of the dye per mole of silver. The resulting emulsion is then coated on a cellulose acetate film support at a coverage of mg. of silver and 400 mg. of gelatin per square foot of support.

A sample of the coated support is then exposed on an Eastman Ib sensitometer using a tungsten light source and processed for 6 minutes at room temperature in Kodak D-19 developer which has the following composition:

G. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite (anhydrous) 90.0 Hydroquinone 8.0 Sodium carbonate (monohydrate) 52.5 Potassium bromide 5.0

Water to make 1.0 liter.

then fixed, washed and dried. The results are listed in Table I hereinafter. Referring thereto, it will be seen that the dye of this example has a maximum density in the unexposed areas of 1.74 and a minimum density in exposed areas of 0.22, a maximum sensitivity at 630 nm. and a relative speed of 725, whereas the control sample similarly prepared and tested but containing no spectral sensitizing dye shows no reversal and has a relative speed less than 1. This result indicates that the dye compound of the above example is especially well suited to function as a spectral sensitizer. It thus provides excellent quality direct positive photographic silver halide emulsions. Excellent magenta images were obtained when the color former 1-(2,4,6 trichlorophenyl)-3,3-(2",4"-di-t-amylphenoxyacetamido)benzamido 5 pyrazolone was incor- 10 porated in the emulsion of this example, the emulsion coated on a support, exposed to a tungsten source through Wratten filter No. 61 and No. 16, and reversal processed as described in Graham et al. US. Pat. 3,046,129, issued July 24, 1962, in Example (a), col. 27, lines 27 et. seq. except that black-and-white (MQ) development was omitted, the color development was reduced to one minute and was conducted in total darkness until after fixing.

EXAMPLE 2 3'-ethyl 1 methyl 5,6-dinitro-2-phenyl-3-indolothiacarbocyanine p-toluenesulfonate 3 formyl-1-methyl-5-nitro-2-phenylindole (1.40 g., 1 mol.), 3-ethyl-2-methyl-6-nitrobenzothiazolium p-toluenesulfonate (1.98 g., 1 mol.) and acetic anhydride (20 ml.) are heated at reflux for 1 minute. The mixture is allowed to cool, then slowly diluted with ether. The solid is collected and washed with ether. After two recrystallizations from methanol, the yield of purified dye is 0.92 g. (28% M.P. 250 C., dec.

This dye containing the desensitizing 1-methyl-5-nitro- Z-phenylindole and 3-ethyl-6-nitrobenzothiazole nuclei is tested for reversal and sensitizing properties by the procedure described in above Example 1. The results are recorded in Table l hereinafter. Referring to the table, densities of 1.78 and 0.03 for the unexposed and exposed areas, respectively, a maximum sensitivity at 550 nm. and a relative speed of 1100 are shown for this dye. Accordingly, the above prepared dye is an excellent electron acceptor and spectral sensitizer for fogged direct positive emulsions.

EXAMPLE 3 1,3-diallyl-1'-methyl 5' nitro-2'-phenylimidazo[4,5-b] quinoxalino-3'-indolocarbocyanine p-toluenesulfonate l CH2CH=CHg HzCH CHz This dye is prepared and purified in the manner described in above Example 2, except that 1,3-diallyl-2- methylimidazo[4,5-b]quinoxalinium p toluenesulfonate (2.18 g., 1 mol.) is used in place of 3-ethyl-2-methyl-6- nitrobenzothiazolium p-toluenesulfonate. The yield of purified dye is 0.65 g. (19%), M.P. 2346 C., dec.

The above prepared dye containing the desensitizing 1-methyl-5-nitro-2-phenylindole and 1,3 diallylimidazo [4,5-b]quinoxaline nuclei is tested for reversal and sensitizing properties by the procedure described in above Example 1. The results are recorded in Table 1 hereinafter. Referring thereto, it will be noted that the densities are 1.98 and 0.03 for the unexposed and exposed areas, respectively, with a maximum sensitivity at 545 nm., and a relative speed of 1150. These results indicate that this dye is an outstanding electron acceptor and spectral sensitizer for fogged direct positive emulsions.

The effectiveness of the dyes of the invention as electron acceptors and spectral sensitizers for fogged direct positive photographic silver halide emulsions is recorded in the following table. The test procedure is described in above Example 1.

It will be apparent from the foregoing disclosure and Examples 1 to 3 that by appropriate selection of intermediates defined by Formulas II, IV, V and VI above, other cyanine dyes of the invention defined by Formulas I and II can be prepared having generally similar properties as electron acceptors and spectral sensitizers, together with improved hold properties, in direct positive photographic emulsions which may also contain colorforming couplers and colored couplers. Typical dyes include the 1,1 dimethyl 5,5 dinitro 2,2 diphenyl- 3,3-indolocarbocyanine salts (e.g., the chloride, bromide, iodide, perchlorate, sulfamate, p-toluenesulfonate, etc. salts); 1,1 dibutyl 5,5 dinitro 2,2 diphenyl 3,3- indolocarbocyanine salts (e.g., the chloride, bromide, iodide, perchlorate, sulfamate, p-toluenesultonate, etc. salts) the 5 chloro 8 ethyl 1,1 dimethyl 5 nitro- 2,2 diphenyl 3,3 indolocarbocyanine salts; the 1,1- dimethyl 5 nitro 5 phenoxy 2,2,8 triphenyl 3,3- indolocarbocyanine salts; the 8 cyclohexyl 5 methoxy- 1,1 dimethyl 5 nitro 2,2 diphenyl 3,3 indolocarbocyanine salts; the 5 ethyl 1,1 dimethyl 5- nitro 2,2 diphenyl 3,3 indolocarbocyanine salts; the 1,1 dimethyl 5 nitro 2,2 diphenyl 3,3 indolocarbocyanine salts; the 3 ethyl l methyl 5,6 dinitro 2 phenyl 3 indolothiacarbocyanine salts (e.g., the chloride, bromide, iodide, percholrate, sulfamate, ptoluenesulfonate, etc. salts); the 3 ethyl 1 methyl- 5,6 dinitro 2 phenyl 3 indoloselenacarbocyanine salts (e.g., the chloride, bromide, iodide, perchlorate, sulfamate, p-toluenesulfonate, etc. salts); the 3 ethyl- 1 methyl 5,6 dinitro 2 phenyl 3 indolo oxacarbocyanine salts (e.g., the chloride, bromide, iodide, perchlorate, sulfamate, p-toluenesulfonate, etc. salts); the 1,3 diethyl 1 methyl 5' nitro 2 phenylimidazo[4,5 b]quinoxalino 3 indolocarbocyanine salts (e.g., the chloride, bromide, iodide, perchlorate, sulfamate, p-toluenesulfonate, etc. salts); the 1 methyl 5- nitro 1,2,3 triphenylimidazo[4,5 b]quinoxalino 3- indolocarbocyanine salt (e.g., the chloride, bromide, idide, perchlorate, sulfamae, p-toluenesulfonate, etc. salts); the l,1',3',3' tetramethyl nitro 2 phenyl 3- indolopyrrolo[2,3 b]pyridocarbocyanine salt; the 1,1- dimethyl 5 nitro 2 phenyl 3 indolothiazolo[4,5- b] quinolinocarbocyanine salt.

The following example illustrates the previously mentioned advantage of the new class of dyes of the invention in reducing the degree of unsensitizing on holding of direct positive emulsions which also contain a colorforming coupler and a colored coupler.

EXAMPLE 4 This example compares the speeds of an incorporated coupler emulsion sensitized with the dye of above Example 3 and two other related dyes containing no nitro substituents, half of these melts being coated immediately after formulation and the other half after a 50-minute hold at 40 C. The test procedure is as follows:

Separate portions of a fogged direct positive silver bromoiodide emulsion prepared in exact accordance with the method described in the photographic test procedure described in above Example 1 are sensitized with the dye of above Example 3 and comparison Dyes A and B. A dispersion of a magenta color-forming coupler such as disclosed in U.S. Pat. No. 2,600,788, for example, 1- 2,4,6'-trichlorophenyl)-3-benzamido-5-pyrazolone plus a colored coupler such as disclosed in U.S. Pat. No. 2,983,608, for example, 1 (2',4,6 tn'chlorophenyD- 3 {4' x(2,4" di tertiaryamylphenoxy) butyra mido] anilino} 4 (4" methoxyphenyl)azo 5- pyrazolone in tricresyl phosphate is added to the emulsion samples. One-half of each melt is coated immediately and the rest is coated after a 50-minute hold at 40 C. The dried coatings are exposed 10 seconds on a Horton Spectograph through a /2 mm. slit and processed in an elon-hydroquinone developer for 6 minutes, fixed, washed and dried. The approximate difierences in speed are tabulated below. These results recorded in Table II below show the very slight speed loss on holding the dye of this invention compared to those of the comparison. dyes.

These results shown in Table II above clearly indicate a factor of 2 or more in favor of the dye of Example 3 for hold purposes, as compared with Dyes A and B. All of the nitro-substituted 2-arylindole dyes of this invention similarly resist unsensitizing in direct positive emulsions containing color former. All photographic color formers tend to cause sensitizing dyes to become unsensitized in direct positive emulsions. All dyes of this invention can, however, be advantageously used with any of the photographic color formers, including monomeric and polymeric color formers, such as pyrazolone, phenolic, heterocyclic, and open chain couplers having a reactive methylene group, such as any of those specifically referred to in the Jelley et al., Fierke et al., Fisher and Wilmanns patents identified below, or in U.S. Pat. 2,600,788 or 2,983,608, to provide emulsions which retain this spectral sensitivity during storage.

The following Examples 5 and 6 illustrate the method for preparing the nitro substituted indole derivatives of the invention.

EXAMPLE 5 1-methyl-5-nitro-2-phenylindole l-methyl-Z-phenylindole (10.35 g., 1 mol.) is dissolved in 99% sulfuric acid (50 ml.). The solution is chilled in an ice-bath to 2 C. and a solution of sodium nitrate (4.25 g., 1 mol.) in 99% sulfuric acid (40 ml.) is added dropwise over a period of about 30 minutes, with stirring, and ice-bath cooling. The temperature rises to a maximum of 8 C. The mixture is stirred a further 5 minutes, then poured onto ice (350 g.), with stirring. The solid is collected and washed with Water. After one recrystallization from dimethyl formamide, the yield of purified material is 9.6 g. (76%), M.P. 1824 C.

EXAMPLE 6 3-formyl- 1-methy1-5 -nitro-2-pl1enylindole Phosphoryl chloride (2.5 ml., 1 mol. +10%) is added to dimethylformamide (20 ml.) and the mixture cooled to room temperature. l-methyl -nitro-2-phenylindole (6.3 g., 1 mol.) is added, and the mixture is stirred and held at 40 for 45 minutes, by which time all the solid is dissolved. The s olution is poured into ice-water (200 ml.) and 5 N NaOH (35 ml.) added. The mixture is heated to boiling, allowed to cool, and the solid collected and washed with water. The yield of cream colored solid is 6.7 g. (96%), MP. 230-2 C.

The following examples further illustrate the preparation of fogged direct positive emulsions and elements with the new cyanine dyes of the invention.

EXAMPLE 7 To 9.0 pounds of a silver chloride gelatin emulsion containing an equivalent of 100 grams of silver nitrate is added 0.017 gram of the dye of above Example 1. The emulsion is coated on a non-glossy paper support, and is flashed with white light to give a density of 1.2 when developed in the following developer, diluted 1 part to 2 parts of water:

Grams N-methyl-p-aminophenol sulfate 3.1 Sodium sulfite, des. 45 Hydroquinone 12 Sodium carbonate, des. 67.5 Potassium bromide 1.9

Water to 1 liter.

The light fogged material thus obtained can be exposed to an image with light modulated by a Wratten No. 15 filter to give a direct positive image. Similar results are obtained when the dye of Examples 2 or 3 is substituted for the aforementioned dye of this example.

EXAMPLE 8 Seven pounds of a silver chloride gelatin emulsion containing the equivalent of 100 g. of silver nitrate is heated to 40 C. and the pH is adjusted to 7.8. Eight ml. of full strength (40%) formalin solution is then added and the emulsion is held at 40 C. for 10 minutes. At the end of holding period, the pH is adjusted to 6.0 and 0.125 g. of the dye of above Example 3 is incorporated therein. The emulsion is then coated on a support, and the element so obtained provides good direct positive images. Similar results are obtained when the dyes of Examples 1 and 2 are used in place of the dye of this example.

By substituting other dye compounds of the invention, as defined by Formulas I and II above, into the procedure of the above examples similar fogged, direct positive photographic silver halide emulsions and photographic elements containing such novel emulsions may be prepared.

The photographic silver halide emulsion and other layers present in the photographic elements made according to the invention can be hardened with any suitable hardener, including aldehyde hardeners such as formaldehyde, and mucochloric acid, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides such as oxy starch or oxy plant gums, and the like. The emulsion layers can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, lubricating materials, stabilizers, speed increasing materials, absorbing dyes, plasticizers, and the like. These photographic emulsions can also contain in some cases additional spectral sensitizing dyes. Furthermore, these emulsions can contain color forming couplers or can be developed in solutions containing couplers or other color generating materials. Among the useful color formers are the monomeric and polymeric color formers, e.g., pyrazolone color formers, as well as phenolic, heterocyclic and open chain couplers having a reactive methylene group. The color forming couplers can be incorporated into the direct positive photographic silver halide emulsion using any suitable technique, e.g., techniques of the type shown in Jelley et al. U.S. Pat. 2,322,027, issued June 15, 1943, Fierke et al. U.S. Pat. 2,801,171, issued July 30, 1957, Fisher U.S. Pats. 1,055,155 and 1,102,028, issued Mar. 4, 1913 and June 30, 1914, respectively, and Wilmanns U.S. Pat. 2,186,849 issued Jan. 9, 1940. They can also be developed using incorporated developers such as polyhydroxybenzenes, aminophenols, 3-pyrazolidones, and the like.

Silver halide sensitized with the dyes of this invention can be dispersed in any of the binders disclosed and referred to in Beavers U.S. Pat. 3,039,873 issued June 19, 1962, col. 13, or polymerized vinyl compounds such as those disclosed in U.S. Pats. 3,142,568; 3,193,386; 3,062,- 674; and 3,220,844, and including the Water insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

I claim:

1. A fogged direct positive photographic silver halide emulsion containing a sensitizing amount of at least one cyanine dye selected from those comprising first and second 5- to 6-membered nitrogen containing heterocyclic nuclei joined by a inethine linkage; the first of said nuclei being a 5-nitro-2-arylindole nucleus joined at the 3-carbon atom thereof to said linkage; and said second nucleus being a desentitizing nucleus joined ata carbon atom thereof to said linkage, to complete said cyanine dye.

2. A direct positive emulsion in accordance with claim 1 wherein said cyanine dye contains a nitro substituted densensitizing nucleus.

3. A direct positive emulsion in accordance with claim 2 wherein said densitizing nucleus is a 5-nitro-2-phenylindole nucleus.

4. A direct positive emulsion in accordance with claim 1 wherein said cyanine dye contains an imidazo[4,5-b] quinoxaline desensitizing nucleus.

5. A direct positive emulsion in accordance with claim 1 in which the said silver halide is present in the form of chemically fogged silver halide grains.

6. A direct positive emulsion in accordance with claim 1 in which the said silver halide is present in the form of reduction and gold fogged silver halide grains.

7. A direct positive emulsion in accordance with claim 1 containing a photographic color former.

8. A direct positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide .grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide50 mg. Acetic acid (glacial)3.47 cc. Sodium acetate1l.49 g. Potassium bromide119 mg. Water to 1 liter.

9. A direct positive, photographic emulsion in accordance with claim 1 which comprises fogged silver halide grains, at least by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.

15 10. A fogged direct positive photographic silver halide emulsion containing a sensitizing amount of at least one cyanine dye selected from those represented by one of the following general formulae:

wherein n represents a positive integer of from 1 to 2; R represents a member selected from the group consisting of hydrogen, an alkyl group and an aryl group, at least one R being hydrogen; R and R each represents an alkyl group; R represents a member selected from the group consisting of an alkyl group, an alkenyl group and an aryl group, R represents an aryl group, R represents a member selected from the group consisting of hydrogen atom, an alkyl group, an alkoxy group, an aryloxy group, a halogen atom, and a nitro group; X represents an acid anion; and Z represents the non-metallic atoms necessary to complete a desensitizing nucleus containing from 5 to 6 atoms in the heterocyclic ring.

11. A direct positive photographic silver halide emulsion in accordance with claim 10 containing at least one cyanine dye selected from those represented by the following general formula:

wherein n is 1; R represents an alkyl group; R represents a member selected from the group consisting of an alkyl group, an alkenyl group and an aryl group; R represents an aryl group; X represents an acid anion; and Z represents the non-metallic atoms required to complete an imidazo [4,5-b1quinoxaline nucleus.

12. A direct positive emulsion in accordance with claim 10 wherein said Z represents the atoms required to complete a desensitizing nucleus selected from the group consisting of a nitrobenzothiazole nucleus, a nitrobenzoxazole nucleus, a nitrobenzoselenazole nucleus, an imidazo[4,5- bJquinoxaline nucleus, a 3,3-dia1kyl-3H-pyrrolo[2,3-b] pyridine nucleus, a 3,3-dialkyl-3H-nitroindole nucleus, a thiazolo [4,5-b1quinoline nucleus and a nitroquinoline nucleus.

13. A direct positive emulsion in accordance with claim 10 in which the said silver halide is present in the form of chemically fogged silver halide grains.

14. A direct positive emulsion in accordance With claim 10 in which the said silver halide is present in the form of reduction and gold fogged silver halide grains.

15. A direct positive emulsion in accordance with claim 10 containing a photographic color former.

16. A direct positive photographic emulsion in accordance with claim 10 which comprises fogged silver halide grains, said grains being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide-50 mg. Acetic acid (glacial)3.47 cc. Sodium acetate-11.49 g. Potassium bromide-119 mg. Water to 1 liter 17. A direct positive photographic emulsion in accordance with claim 10 which comprises fogged silver halide grains, at least by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.

18. A direct positive photographic emulsion in accordance with claim 10 containing a cyanine dye selected from the group consisting of 1,1'-dimethyl-5,5'-dinitro-2,2'-diphenyl-3,3'-indolocarbocyanine salt; 3'-ethyl-l-methyl- 5,6-dinitro-2-phenyl-3-indolothiacarbocyanine salt; and 1,3 diallyl 1 -'methyl-5-nitro-2'-phenylimidazo [4,5-b] quinoxalino-B-indolocarbocyanine salt.

19. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 1.

20. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 8.

21. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 9.

22. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 10.

23. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 16.

24. A photographic element comprising a support having thereon at least one layer containing a direct positive emulsion of claim 17.

References Cited UNITED STATES PATENTS 2,930,694 3/1960 Coenen et a1. 96-106 3,250,618 5/1966 Stewart et a1 96-101 3,314,796 4/1967 Gatze et a1. 96-101 OTHER REFERENCES The theory of the Photographic Process, 3rd edition, Mees & James, MacMillan Co., New York, TR M4t 1966 c2, page 259.

NORMAN G. TORCHIN, Primary Examiner R. E. FIGHTER, Assistant Examiner US. Cl. X.R

5232 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,582, 343 Dated June 1 1971 Inventor(s) John D. Mee

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 11, "E L" should read ---25---.

Column 14, line 38, densensitizing" should read ---desensitizing---; line &0, densitizing" should read ---desensitizing---.

Column 16, line 52, insert:

--25, A direct positive photographic silver halide emulsion sensitized with the combination of thiourea dioxide and potassium chloroaurate, said emulsion being spectrally sensitized with 1,3-diallyl-l'-methyl-5- nitro-E -phenylirnidazo/E,5-b7quinoXalino-3'-indolocarbocyanine p-toluenesulfo fiate and containing the photographic color former l-(2',4,6-trichlorophenyl)-3-benzamido5- pyrazolone.-

Signed and sealed this 2nd day of May 1972.

(SEAL) Attest:

EDWARD MJLETOHER IR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

